WASHINGTON, Dec 7 (Reuters) - The U.S. Environmental
Protection Agency on Monday cleared the way for regulation of
greenhouse gases without new laws passed by Congress,
reflecting President Barack Obama's commitment to act on
climate change as a major summit opened in Copenhagen.

The EPA ruling that greenhouse gases endanger human health,
widely expected after it issued a preliminary finding earlier
this year, will allow the agency to regulate planet-warming
gases even without legislation in Congress.

The agency could begin to make rules as soon as next year
to regulate emissions from vehicle tailpipes, power utilities
and heavy industry under existing laws.

Obama and his Democratic allies in Congress will still
pursue legislation in Congress, which has been slow to act. But
the EPA move gave a timely push to the president's aims of
securing short-term limits to harmful emissions.

It was expected to inject some optimism into the two-week
United Nations meeting in Copenhagen, which Obama is due to
attend next week, but was criticized by some U.S. business
groups who fear it could push up costs.

"EPA has finalized its endangerment finding on greenhouse
gas pollution and is now authorized and obligated to make
reasonable efforts to reduce greenhouse pollutants," said Lisa
Jackson, the EPA administrator. "This administration will not
ignore science or the law any longer."

The Supreme Court ruled in 2007 that the EPA had the right
to regulate emissions of the gases under the Clean Air Act. But
under the administration of former President George W. Bush,
the EPA said Congress was the right place to frame action.

Business groups said the EPA announcement would hurt the
economy and endanger jobs just as the country emerges from a
deep recession.

Legislation by Congress would be more palatable politically
for Obama, because it would represent a compromise between
business, politicians and other interests rather than through
an imposed ruling.

STRONGER HAND IN COPENHAGEN

The EPA ruling applies to six gases scientists say
contribute to global warming, including the main one, carbon
dioxide.

There had been fears that Obama, who has made fighting
climate change one of his priorities, would arrive almost empty
handed at the U.N. conference because climate legislation has
stalled in Congress.

"The EPA move strengthens Obama's hand at Copenhagen," said
Joe Mendelson, global warming policy director at the National
Wildlife Federation. "It gives him additional authority that if
Congress doesn't pass climate legislation, the agency can put
the country on the path to meet his climate goals."

Obama will pledge at Copenhagen that the United States, the
world's second largest emitter of greenhouse gases, will cut
emissions by roughly 17 percent by 2020 from 2005 levels.

World leaders hope to reach an agreement at the meeting on
getting rich and developing countries to share the burden in
fighting climate change.

The climate bill has been delayed in the U.S. Senate by a
debate over a sweeping reform of healthcare, but lawmakers hope
to pass a bill in the spring. Climate legislation passed
narrowly in the House of Representatives in June.

The Obama administration has always said it prefers
legislation over action by the EPA.

CONGRESSIONAL ACTION

If the EPA acts alone it could face a slew of legal
challenges, including from business groups who say the action
would overstep the administration's authority, as well as from
environmentalists who seek stronger steps.

But the administration had pressed the EPA to prod business
to support efforts in Congress, and to show the world
Washington is committed to fighting climate change.

Democratic Senator John Kerry said the EPA move was meant
to spur Congress to act. But he said "imposed regulations by
definition will not include the job protections and investment
incentives we are proposing in the Senate today."

Republicans said the move was equivalent to imposing an
energy tax. "By seeking to sharply curtail carbon dioxide (and
thus energy usage), the EPA is in effect working to decrease
economic activity," the Republican Study Committee said.

One business group was quick to criticize the EPA.

Keith McCoy, vice president of energy policy at the
National Association of Manufacturers said the EPA was moving
forward with an agenda that will put additional burdens on
manufacturers, cost jobs and drive up the price of energy."

The EPA decision, which now will be open for public review,
does not preclude legislation. Any new regulations could take a
long time to implement, giving Congress room to act.

Still, big industry could learn about changes soon.
Jackson said car makers will know by the end of March about
required increases in fuel economy standards for cars built for
the 2012 model year.

"All industries will be called upon to reduce carbon
emissions," said Dave McCurdy, chief executive of the Alliance
of Automobile Manufacturers.

An administration proposal unveiled in September would
require a boost fuel efficiency by 40 percent by 2016 and aim
to cut carbon emissions by 21 percent by 2030.
(Additional reporting by Ayesha Rascoe, Roberta Rampton,
Deborah Zabarenko, Tom Doggett, Tom Ferraro in Washington and
Richard Cowan in Copenhagen; Editing by Simon Denyer and Chris
Wilson)